1. Field of the Invention
This application relates generally to semiconductor devices and patterned device fabrication. More particularly, this application relates to the formation of multi-component oxide heterostructures (MCOH) using patterned atomic layer deposition (ALD) and patterned etch and metallization to produce ultra-high density MCOH nano-electronic devices.
2. Description of the Related Art
A high-mobility two-dimensional electron gas (2DEG) at the interface between a polar oxide (e.g., LaAlO3) and a non-polar oxide (e.g., SrTiO3) has fueled significant interest in oxide-based electronics. The interface between these materials can be switchable between a metallic and insulating state when the LaAlO3 thickness is exactly 3 unit cells. Some suggest this occurs due to charge interactions between the different layers. In LaAlO3, the valences of the LaO layer carry a net charge of +e and the AlO2 layer carries a net charge of −e, resulting in a neutral unit cell. In contrast, the individual layers in SrTiO3 are charge neutral. When a LaO+ layer is joined to a TiO20 neutral layer, a polar discontinuity occurs that can cause charge rearrangement where conceptually half an electron is transferred from the LaO layer to the TiO2 layer. Since the AO—BO2 stacking sequence is maintained in perovskite heterostructures along the [001] direction, a polarity discontinuity arises at the LaAlO3—SrTiO3 interface. Because the titanium (Ti) ion allows for mixed valence charge compensation, this results in the net transfer of electrons (nominally 0.5 electron per two-dimensional unit cell) from LaAlO3 to SrTiO3 across the interface. Other evidence suggests that vacancies created in the substrate during growth are responsible for the transport properties observed; however, a sole vacancy model does not explain the strikingly high mobility observed. In certain circumstances, the values can be as high as ne=1014 cm−2 and μ=104 cm2V−1s−1. It may also be possible that both vacancies and polar discontinuities are responsible for these observations. In any case, such interfacial conductance in MCOH can be patterned for a small number of devices at scales approaching one nanometer using a conducting atomic-force microscope (AFM) probe.